The present invention relates to an electrolyte and a fuel cell, a Li secondary battery, a secondary battery and a primary battery using the electrolyte, more specifically, an electrolyte excellent in hydroxide ion conductivity and durability and a fuel cell, a Li secondary battery, a secondary battery and a primary battery using such an electrolyte.
Alkaline fuel cells are fuel cells using, as the electrolyte thereof, a hydroxide ion conductor such as an alkaline electrolyte or anion exchange polymer electrolyte.
Alkaline fuel cells are used in an alkaline atmosphere so that inexpensive electrode catalysts such as nickel can be used for them. In addition, they do not need an expensive separator such as Ti because the corrosion environment in the alkaline atmosphere is weaker than that in the acidic atmosphere. Alkaline fuel cells can therefore actualize cost reduction of a fuel cell system compared with solid polymer fuel cells using a proton exchange polymer electrolyte.
As to anion exchange polymer electrolytes usable as an electrolyte for alkaline fuel cells and production process thereof, various proposals have conventionally been made.
For example, Patent Document 1 discloses an allylamine-allylsulfonic acid copolymer which is not an anion exchange polymer electrolyte but contains a structural unit derived from monoallylamine or diallylamine and a structural unit derived from an allylsulfonic acid compound.
Patent Documents 2 and 3 disclose a crosslinked polymer containing a tertiary amine and/or a quaternary ammonium salt and having a tertiary amine structure at both ends of at least one crosslinked site.
According to these documents, a crosslinked polymer having such a structure is excellent in thermal decomposition resistance.
Patent Document 4 discloses a hydrocarbon-based anion exchange membrane available by:
(a) filling the void portion of a hydrocarbon-based porous film with a polymerizable composition containing a vinylcarboxylic acid amide, a crosslinkable polymerizable monomer, and a polymerization initiator and polymerizing and curing the polymerizable composition in the void portion,
(b) hydrolyzing the carboxylic acid amide group into a corresponding amino group, and
(c) converting the amino group into the corresponding quaternary ammonium salt by using an alkylating agent.
According to this document, the hydrocarbon-based anion exchange membrane having such a constitution has a high ion exchange capacity and high conductivity.
Patent Document 5 discloses an anion exchange resin having a styrene skeleton as a main chain and having an aromatic ring to which a quaternary ammonium group is bonded via an alkylene chain; and a hydrocarbon-based anion exchange membrane obtained by filling this anion exchange resin in the void portion of a porous film.
According to this document, a hydrocarbon-based anion exchange membrane having such a structure has a large ion exchange capacity, a high water content, and small membrane resistance.
Patent Document 6 discloses a polymer electrolyte composition which is not an anion exchange polymer electrolyte but contains a cation exchange resin having a sulfonic acid group and an anion exchange resin having at least one heterocyclic group containing a cationic nitrogen atom.
According to this document, the polymer electrolyte composition having excellent flexibility while having practically sufficient proton conductivity can be obtained by adding a small amount of an anion exchange resin to a cation exchange resin.
Non-patent Document 1 discloses a copolymer of diallylamine and CF2CFCl. According to this document, the resulting copolymer has excellent high-temperature durability (Tg: exceeding 200° C.) but low OH− conductivity.
Non-patent Document 2 discloses a process of subjecting a cyclooctene ring added with a quaternary ammonium salt to ring opening metathesis polymerization.
Further, it is generally known that an anion exchange resin containing a benzyltrimethyl ammonium portion is thermally instable under alkali conditions. For example, Non-patent Document 3 has reported that a residual ratio of such an anion exchange resin is 79% after placed under the conditions of 100° C. for 13 days.
It is the common practice to use, as a polymer electrolyte to be used for alkaline fuel cells, an anion exchange resin obtained by introducing an alkyl halide group such as benzyl chloride in a phenyl portion of a polystyrene structure or the like and then quaternizing the resulting product with trimethylamine. An anion exchange resin equipped with such a structure, however, lacks long-term durability because the benzyl position (or alkyl chain) at which the trimethylamine group is bonded to a phenyl group drops off as a result of thermal decomposition.
In particular, when an anion exchange resin equipped with this structure is used as an electrolyte for alkaline fuel cells, use of hydrazine as a fuel causes oxidation of the benzyl position or alkyl portion with hydrazine and oxygen and facilitates elimination of an ion group (trimethylamine). As a result, hydroxide ion conductivity of the electrolyte decreases, leading to lack of long-term durability.